(a) Field of the Invention
The invention relates to a long-acting galenical formulation of GRF peptides, GRF and/or GRF analogs having a long-lasting and prolonged activity.
(b) Description of Prior Art
Growth hormone (GH) or somatotropin, secreted by the pituitary gland constitute a family of hormones which biological activity is fundamental for the linear growth of a young organism but also for the maintenance of the integrity at its adult state. GH acts directly or indirectly on the peripheral organs by stimulating the synthesis of growth factors (insulin-like growth factor-I or IGF-I) or of their receptors (epidermal growth factor or EGF). The direct action of GH is of the type referred to as anti-insulinic, which favors the lipolysis at the level of adipose tissues. Through its action on IGF-I (somatomedin C) synthesis and secretion, GH stimulate the growth of the cartilage and the bones (structural growth), the protein synthesis and the cellular proliferation in multiple peripheral organs, including muscles and the skin. Through its biological activity, GH participates within adults at the maintenance of a protein anabolism state, and plays a primary role in the tissue regeneration phenomenon after a trauma.
The decrease of GH secretion with the age, demonstrated in humans and animals, favors a metabolic shift towards catabolism which initiates or participate to the aging of an organism. The loss in muscle mass, the accumulation of adipose tissues, the bone demineralization, the loss of tissue regeneration capacity after an injury, which are observed in elderly, correlate with the decrease in the secretion of GH.
GH is thus a physiological anabolic agent absolutely necessary for the linear growth of children and which controls the protein metabolism in adults.
The secretion of GH by the pituitary gland is principally controlled by two hypothalamic peptides, somatostatin and growth hormone-releasing factor (GRF). Somatostatin inhibits its secretion, whereas GRF stimulates it.
The human GH has been produced by genetic engineering for about ten years. Until recently most of the uses of GH were concerned with growth delay in children and now the uses of GH in adults are studied. The pharmacological uses of GH and GRF may be classified in the following three major categories.
Children Growth
Treatments with recombinant human growth hormone have been shown to stimulate growth in children with pituitary dwarfism, renal insufficiencies, Turner's syndrome and short stature. Recombinant human GH is presently commercialized as an "orphan drug" in Europe and in the United States for children's growth retardation caused by a GH deficiency and for children's renal insufficiencies. The other uses are under clinical trial investigation.
Long Term Treatment for Adults and Elderly Patients
A decrease in GH secretion causes changes in body composition during aging. Preliminary studies of one-year treatment with recombinant human GH reported an increase in the muscle mass and in the thickness of skin, a decrease in fat mass with a slight increase in bone density in a population of aged patients. With respect to osteoporosis, recent studies suggest that recombinant human GH does not increase bone mineralization but it is suggested that it may prevent bone demineralization in post-menopausal women. Further studies are currently underway to demonstrate this theory.
Short Term Treatment in Adults and Elderly Patients
In preclinical and clinical studies, growth hormone has been shown to stimulate protein anabolism and healing in cases of burn, AIDS and cancer, in wound and bone healing.
GH and GRF are also intended for veterinary pharmacological uses. Both GH and GRF stimulate growth in pigs during its fattening period by favoring the deposition of muscle tissues instead of adipose tissues and increase milk production in cows, and this without any undesired side effects which would endanger the health of the animals and without any residue in the meat or milk being produced. The bovine somatotropin (BST) is presently commercialized in the United States.
Most of the clinical studies presently undertaken were conducted with recombinant GH. The GRF is considered as a second generation product destined to replace in the near future the uses of GH in most instances. Accordingly, the use of GRF presents a number of advantages over the use of GH per se.
Physiological Advantages
Growth hormone (GH) is secreted by the pituitary gland in a pulse fashion, since this rhythm of secretion is crucial for an optimal biological activity, the administration of GH to correspond to its natural mode of secretion is difficult to achieve. When GRF is administered in a continuous fashion as a slow releasing preparation or as an infusion, it increases GH secretion while respecting its pulsatility.
The recombinant GH which is presently commercialized is the 22 kDa form whereas GRF induces the synthesis and secretion from the pituitary gland of all the chemical isomers of GH which participate in a wider range of biological activities.
A treatment with GH results in a decreased capacity of the pituitary gland to secrete endogenous growth hormone, and the GH response to GRF is diminished after such a treatment. On the contrary, a treatment with GRF does not present this disadvantages, its trophic action on the pituitary gland increases this gland secreting capacity in normal animals and in patients with somatotroph insufficiency.
Economical Advantages
The production of GH by genetic engineering is very expensive for clinical use. In particular, there are risks of contamination of these commercial preparation with material from the bacterial strain used. These bacterial contaminants may be pyrogens or may result in immunogenic reactions in patients. The purification of the recombinant product is effected by following a plurality of successive chromatography steps. The drastic purity criteria causes multiple quality control steps.
The synthesis of GRF is of chemical nature. The synthesis effected in a solid phase and its purification is carried out in a single step using high performance liquid chromatography (HPLC). Also the quantity of GRF to be administered is much less than the quantity of GH for the same resulting biological activity.
Even with all these advantages, GRF is still not commercialized to date as a therapeutic agent mainly because of its chemical instability. The human GRF is a peptide of 44 amino acids of the following sequence:
Tyr Ala Asp Ala Ile Phe Thr Asn Ser Tyr Arg Lys Val Leu Gly Gln (SEQ ID NO:1) 1 5 10 15 Leu Ser Ala Arg Lys Leu Leu Gln Asp Ile Met Ser Arg Gln Gln Gly 20 25 30 Glu Ser Asn Gln Glu Arg Gly Ala Arg Ala Arg Leu-NH.sub.2. 35 40 The minimum active core is hGRF (1-29)NH.sub.2 Tyr Ala Asp Ala Ile Phe Thr Asn Ser Tyr Arg Lys Val Leu Gly Gln (SEQ ID NO:2) 1 5 10 15 Leu Ser Ala Arg Lys Leu Leu Gln Asp Ile Met Ser Arg. 20 25
Clinical studies with children and adults have confirmed that natural hGRF (1-44)NH.sub.2 or the active fragment hGRF (1-29)NH.sub.2 are not potent enough to produce equal effects corresponding to those of recombinant GH.
It is now well documented that hGRF has a very short half-life in serum, being rapidly enzymatically cleaved and inactivated following its injection. As a result, numerous studies have reported that hGRF or its analogs have to be injected daily or several times a day in human and animals to effectively exert its anabolic effect through growth hormone and IGF-I releases. This kind of treatment regimen requiring multiple injections is very time consuming and uncomfortable for the patients, which has so far hampered the clinical use of hGRF and analogs.
Several GRF preparations have been described (U.S. Pat. Nos. 5,137,669, 5,039,660 and 5,192,741, respectively issued on Aug. 11, 1992, Aug. 13, 1991 and Mar. 9, 1993), in which GRF is mixed with various carriers to increase its duration of action. However, all those preparations incorporate carriers that may induce immune or inflammatory reactions following administration.
It would be highly desirable to be provided with a long-acting galenical formulation of GRF peptides, GRF and/or GRF analogs having a long-lasting and prolonged activity without the addition of any carrier.